Both Mac and Windows have basic image editors which you can use to modify images, as discussed below.

Super Easy Editing

We have also found that the free site ?http://www.picnik.com provides easy access to the most common photo editing tools.

Resizing and Cropping on a Mac

Apple's Preview program (on your computer at Macintosh HD -> Applications -> Preview) is a simple, but very capable program for not only viewing files, but for performing some basic graphic editing, too. A good help link from Apple is at:http://support.apple.com/kb/ht2506